Optical instruments such as cameras and/or video cameras have been so commonly used in daily life that variations of them have been widely incorporated in portable electronic devices such as smart phones, tablet computers, as well as mobile surveillance units such as digital image and/or video recorders for home use or installable in vehicles or in buildings. Very often, these optical instruments or their variations comprise one or more light transmissive optical components such as optical lenses, and during their manufacturing process, inspection of these optical lenses for defects has always been challenging. Lens inspection generally requires specialized skills of the inspector, and the process can be highly time and labor intensive. Existing methods may involve manual and visual checking for defects at the lens such as black spots, scratches, dust or dirt particles, air bubbles, flow marks and/or other injection or coating defects. Quality of such inspections is thus largely dependent on judgement of the inspecting individual, which could be subjective and inconsistent. Accuracy of the inspections may further be compromised, especially during a mass production process where a large number of lenses are to be manually and visually inspected. It would be understandable that continuous and repetitive visual checking for long hours may cause vision fatigue or even damage to one's eyesight, which may further deteriorate quality and reliability of the inspection.